1. Field of the Invention
The present invention relates to a new type of non-tensioned shaker filter for use in a shale shaker such as shakers designed to remove solids from drilling fluids. More specifically, the present invention is a new type of corrugated filter that does not employ a rigid backing material incorporated into the filter and that may be used with a shaker that is provided with non-tensioned means for securing a filter to a shaker. For example, one such non-tensioned means for securing a filter to a shaker is taught in U.S. Pat No. 5,690,826, a patent that was granted to the inventor of the present invention.
2. Description of the Related Art
In the drilling industry, shakers are used to remove large amounts of coarse, drilling cuttings from drilling fluids so that the drilling fluids may be reused or recirculated within the well that is being drilled. The cuttings are generally filtered out of the drilling fluid on a series of canted filters provided within the shaker. Dirty drilling fluid is introduced onto a top side of a front screen of a series of screens provided in the shaker. The drilling fluid flows through the filters and the cuttings, or tailings as they are sometimes called, remain on the topside of the filters. The drilling fluid that has passed through the filters is now clean of coarse debris and is ready to be cleaned via other processes prior to being ready for reuse. Due to the shaking action of the shaker, the tailings which were separated out of the drilling fluid are propelled rearwardly along the front canted filter until they reach the back edge of the first filter in the series and fall down to the adjacent front edge of the next filter in the series. The tailings move rearward along the next canted filter in the series as described for the front filter until finally, when the tailings reach the back edge of the last filter in the series, the tailings are relatively dry and they fall off the last filter into a tailings disposal portion of the shaker and are thus eliminated from the shaker.
Prior art shaker filters have, until now, always been under tension when they were in use. Prior art shaker filters were always one of the two common types of filters, i.e. either the hookstrip type filter or the rigid frame type filter. The rigid frame type filter is also known as the pretensioned type filter.
Hookstrip type filters have a rigid perforated backing, also sometimes referred to as an apertured plate or metal back, that is provided as an integral part of the filter in association with the filter medium. A rigid backing is necessary for the hookstrip type filters to function because these filters are secured between opposite walls of the shaker under a great deal of tension. This tension is placed on hookstrip type filters by means of clamps or drawbars that attach to and pull on the hook portion of the hookstrip type filter. A hook portion is provided on each of the two opposite side edges of the hookstrip type filter, and the drawbars that engage these hook portions are provided on the shaker. Tensioning bolts attach to the drawbars and secure the hookstrip type filters to the walls of the shaker.
The tensioning bolts are tightened in order to place the hookstrip type filters under tension, thereby pulling the hookstrip type filters tightly between the opposite walls of the shaker and forcing the hookstrip to be pulled downward over arched support components provided on the shaker. The arched support components extend between the opposite walls of the shaker and are secured to the walls of the shaker. The arched supports extend transverse to the longitudinal axis of the filters If the hookstrip type filters were not provided with a rigid backing, they would not be able to withstand the tension that is placed on them, and they would be pulled apart and destroyed when tension was applied to them.
The rigid frame type is also referred to as a pretensioned type filter because when the filter is manufactured, the filter medium is secured upon its rigid frame under tension. The rigid frame type filter is secured to the shaker with clamps in a matter similar to that previously described for tensioned filters or with wedges. However, in the case of rigid frame type filters, the clamps and wedges serve merely to secure the rigid frame type filters to the shaker and do not serve to further tension the filters since no further tensioning of pretensioned type filters is needed.
One of the problems encountered with these prior art filters is that they must, by their very nature, employ rigid backings or other similar types of apertured plates as an integral part of the filter. All prior art corrugated filters must be provided with a rigid backing in order for the corrugations to withstand the tension that is applied to them when they are secured to the shaker. Generally these rigid backings are constructed of metal and may be comprised of perforated metal sheets, or comprised of woven metal bands or slats. Adding these backings to the filters, as an integral part of the filters, significantly increases the cost of each of these filters. Additionally, whenever one of these types of filters must be disposed of, these integrated backings, which are not biodegradable or incinerable, increase the cost of disposal and increase the volume of material that must be disposed.
Another problem with these prior art filters is associated with how they are secured to the shaker. As previously described, each prior art filter is secured to the shaker by means of bolts and associated clamps. A series of multiple bolts and clamps or drawbars are necessary in order to secure each filter in place within a shaker.
In order to remove a filter so that the filter can be inspected, cleaned, or replaced, it is necessary to perform the following steps. First all of the bolts must be loosened. Then the drawbars must be knocked loose from each side of the shaker. The filter then can be removed and replaced with a new filter. The drawbars are then reinstalled, and all of the bolts are retighten. For a shaker that employs a series of three screens, the total shaker downtime required for filter maintenance can be as long as 45 minutes. Each time the shaker is out of operation, drilling must cease or a second shaker must be employed. Thus, downtime for a shaker translates into a significant financial burden due to the forced downtime of the drilling rig or additional expense of a second shaker.
A further problem with prior art filters of the hookstrip type is that they are curved upward in their center relative to their sides due to the tensioning of the screens over the support components. Pretensioned or rigid frame types of filters are generally not arched in this manner. The upward curvature of hookstrip type filters is caused by the arched support components that are provided under the filters. The arched support components are provided in order to support the filters when fluid is introduced onto the top surfaces of the filters and to prevent flexing of the filters when the filters are shaken in the shaker. As previously described, prior art filters of the hookstrip type are tensioned over these support structures when the filters are secured to the shaker, thus causing the top surface of the filters to be arched. Because the filters are arched from side to side, this arched or curved configuration disproportionately distributes the fluid flow over the surface of the screen, with the outer edge areas nearest the shaker sidewalls receiving the much greater portion of the flow. This overloading of the outer areas causes early clogging, or "blinding", a common problem requiring more frequent cleaning or screen replacement, as well as inefficient filtering when compared with a nonarched, i.e., flat, filters.
The present invention addresses these problems by providing a filter which does not employ integral metal support structures but instead relies upon the support proved from a non-tensioning receiving assembly that is provided on the shaker. A non-tensioning receiving assembly may be provided either as an integral art of new shakers or may be provided as a retrofit assembly for existing shakers. One type of non-tensioning assembly is taught in U.S. Pat. No. 5,690,826 and is provided with a hinged lid which can be easily opened and reclosed, allowing filters constructed in accordance with the present invention to be removed and replaced within the assembly in a matter of seconds. With such a short replacement time, the present filters can be replaced with only minimal downtime.
Filters constructed in accordance with the present invention are corrugated, which increases the surface area of the filters and thus increases their efficiency. Even though these filters do not have an integral backing, they can retain their corrugations during use because they are not placed under side-to-side tension, such as the tension that is exerted on prior art shaker filters.
Although the filters are corrugated and therefore are provided with undulations, the filters of the present invention remain flat while in use in the shaker, i.e. the filters are not arched in the middle relative to the sides of the filter. This allows them to function more efficiently than prior art, hook type filters that must be in an arched configuration when in use in shakers.
Due to the elimination of the integral metal support structure in the present filters, the cost of producing the present filters is greatly reduced over the cost of producing prior art shaker filters. Also, the cost of disposing of the present filters is also greatly reduced over the disposal costs for prior art shaker filters since the present filters consist almost entirely of nothing more than the fragile, lightweight wire mesh.